CN103199801B - Turbine flow sensor preamplifier with nonlinear compensation and compensation method - Google Patents

Abstract

The invention relates to a preamplifier of a turbine flow sensor with nonlinear compensation and a compensation method, comprising a shaping amplifier circuit, a signal input processing unit, an NXP51 series single-chip microcomputer, and an output signal processing unit. The sensor coil induces an alternating signal of magnetic flux to generate an alternating induced potential, that is, an electric pulse signal. After being shaped and amplified by the circuit, it is output through the signal input processing unit, NXP51 series single-chip microcomputer, and output signal processing unit. The non-linear compensation function is all completed in the preamplifier, without changing the original average meter coefficient placed in the display (integrating) instrument; nor changing the calculation method of the display (integrating) instrument for instantaneous flow and cumulative flow, increasing generality. The preamplifier of the present invention improves the measurement accuracy of the turbine flow sensor to within ±0.5% to 1%, and expands the range to 10:1 to 20:1, thereby overcoming the nonlinear error of the turbine flowmeter when measuring small flow Big question.

Description

Turbine flow sensor preamplifier with nonlinear compensation and compensation method

technical field

The invention relates to an amplifier, in particular to a turbine flow sensor preamplifier with nonlinear compensation and a compensation method.

Background technique

The turbine flow sensor is used for fluid flow measurement and consists of an impeller, a magnetic steel coil, a preamplifier, etc. At present, the flow measurement mechanism of the turbine flow sensor is: the turbine flow sensor is installed in the pipeline of the measured flow, and the flowing fluid makes the impeller rotate; the magnetic steel coil generates a magnetic field, and the impeller rotates to cut the magnetic force line, so that the magnetic flux of the coil occurs periodically. Changes, thereby generating an alternating induction potential, that is, an electric pulse signal. The output electric pulse signal is amplified and shaped by the preamplifier to generate a continuous rectangular wave pulse signal with a certain amplitude. The pulse signal is transmitted to the display instrument, and after calculation, the instantaneous flow and cumulative flow of the measured fluid are displayed.

The display instrument obtains the measured fluid flow rate according to the pulse signal frequency output by the preamplifier:

(1)

It is the average meter coefficient within the range of the turbine flow sensor, indicating the number of pulses output by the sensor when the flow per unit volume passes through the turbine flow sensor, and is calculated by the following formula:

(2)

In the formula, K _{max and} K _min are respectively the maximum value and minimum value of the meter coefficient among the n calibration points.

The nonlinear error and repeatability error of the sensor are calculated according to the following formulas:

(3)

(4)

At present, the repeatability of the turbine flow sensor can generally be a few ten-thousandths, while the nonlinear error is generally ±1% to ±1.5%, and the range is 6:1. When the flow rate is small, the nonlinear error of the turbine flow sensor is very large. Therefore, the turbine flow sensor can only measure a section of the approximate straight line in the q - K characteristic curve, which limits the accuracy and range of flow measurement.

Contents of the invention

The present invention aims at the problem of the nonlinear error caused by the nonlinearity of the instrument coefficient in the turbine flow sensor, and proposes a turbine flow sensor preamplifier with nonlinear compensation and a compensation method to correct the nonlinear error in real time and expand the turbine flow Sensor range, improve flow measurement accuracy.

The technical solution of the present invention is: a turbine flow sensor preamplifier with nonlinear compensation, including a shaping amplifier circuit, a signal input processing unit, an NXP51 series single-chip microcomputer, an output signal processing unit, and the sensor coil induces a magnetic flux alternating signal, The alternating induction potential is generated, that is, the electric pulse signal. After being shaped and amplified, it is output through the signal input processing unit, NXP51 series single-chip microcomputer, and output signal processing unit.

A compensation method for a turbine flow sensor preamplifier with nonlinear compensation, comprising a turbine flow sensor preamplifier with a compensation function, comprising the following steps:

1) NXP51 series single-chip microcomputer can get ( n -1) straight lines according to n calibration points ( f _i , K _i , i =1,2,…, n ), the i -th ( i =1,2,3… n - 1) The linear equation of the instrument coefficient K of the section is:

When f _{i ,} K _i _ are respectively the i -th flow calibration point, the output frequency of the turbine flow sensor and the corresponding meter coefficient, the measured pulse frequency f is divided by the meter coefficient K calculated by the above formula, and the non- Flow q ₀ after linear compensation:

The output pulse frequency f _out after compensation is:

In the formula, f is the frequency detected by the sensor;

is the average meter factor within the compensation range, ,

In the formula, K _{max and} K _min are respectively the maximum value and minimum value of the instrument coefficient among the calibration points of n points within the compensation range, forming a comparison table between the detected sensor frequency f and the compensated pulse frequency f _out ;

2) The sensor coil induces the magnetic flux alternating signal to generate the alternating induced potential, that is, the electric pulse signal, which is shaped and amplified by the circuit; the signal is input to the processing unit, and then input to the NXP51 series single-chip microcomputer, and the NXP51 series single-chip microcomputer collects the input pulse frequency and judges Whether the input frequency is within the compensation range, if so, find out the corresponding compensated pulse frequency f _out according to the table obtained in step 1), and output it through the output signal processing unit; if not, output the collected input pulse signal directly to the output Output after signal processing unit.

The beneficial effects of the present invention are: the preamplifier of the turbine flow sensor with compensation and the compensation method of the present invention, the non-linear compensation functions are all completed in the preamplifier, and the original average instrument placed in the display (integrating) instrument is not changed. Coefficient; does not change the calculation method of the display (integrating) instrument for instantaneous flow and cumulative flow, which increases the versatility. The preamplifier of the present invention improves the measurement accuracy of the turbine flow sensor to within ±0.5% to 1%, and expands the range to 10:1 to 20:1, which overcomes the problem of large nonlinear errors of the turbine flowmeter when measuring small flow rates .

Description of drawings

Fig. 1 is the schematic diagram of the preamplifier circuit of the turbine flow sensor with nonlinear compensation in the present invention;

Fig. 2 is the main program flow chart of NXP51 single-chip microcomputer of the present invention;

Fig. 3 is a flow chart of the pulse acquisition and compensation interrupt service program of the present invention;

Fig. 4 is a flow chart of the compensation pulse output interrupt service program of the present invention.

detailed description

As shown in Figure 1 is the schematic diagram of the preamplifier circuit of the turbine flow sensor with nonlinear compensation. The preamplifier circuit of the turbine flow sensor with nonlinear compensation function includes: signal input processing unit 1, NXP51 series microcontroller 2, output Signal processing unit 3. The signal input processing unit 1 processes the pulse signal input by the P port, and performs limiting, filtering and shaping processing on the signal. The output signal processing unit 3 processes the output pulse signal of the Pout port, amplifies and shapes the signal. The input processing unit 1 is connected to the NXP51 series microcontroller 2, and then output through the output signal processing unit 3. Traditional turbine flow sensor preamplifiers only shape and amplify the input pulse. The turbine flow sensor preamplifier with nonlinear compensation function adds an intelligent chip to the traditional preamplifier. The preamplifier of the turbine flow sensor with nonlinear compensation function not only shapes and amplifies the electric pulse signal induced by the coil, but also performs intelligent nonlinear compensation calculation on the collected pulse. In Fig. 1, the input signal of the P terminal is the output signal of the traditional preamplifier, that is, the electrical pulse signal after amplifying and shaping, and the P _out terminal is the output terminal of the preamplifier of the turbine flow sensor with nonlinear compensation function, and the output signal is used for Display the input signal of the instrument to display the instantaneous flow and cumulative flow.

Turbine flow sensor preamplifier control with nonlinear compensation includes input pulse frequency detection, nonlinear compensation, pulse output. The compensation algorithm is a piecewise linear compensation method, and its software implementation adopts a look-up table method, and the table is the pulse frequency after compensation. The calculation method of the pulse frequency after compensation is as follows: According to n calibration points ( f _i , K _i , i =1,2,…, n ), ( n -1) straight lines can be obtained, and these ( n -1) straight lines can be obtained To approximate the actual K - f curve. The straight line equation of segment i ( i =1,2,3… n -1) is:

(5)

The measured pulse frequency f is divided by the meter coefficient K calculated by the above formula, and the flow q ' after nonlinear compensation can be obtained:

(6)

Combining equations (5) and (6), the compensated pulse frequency f _out of the preamplifier output of the turbine flow sensor with nonlinear compensation is:

(7)

In the formula, f is the frequency detected by the sensor; f _out _ is the output frequency of the preamplifier of the turbine flow sensor with nonlinear compensation, f _{i ,} K _i _ are the output frequencies of the turbine flow sensor at the ith flow calibration point respectively and the corresponding meter coefficients; _ is the average meter coefficient within the range, calculated by formula (2).

As shown in Figure 2, it is the main program flowchart of NXP51 single-chip microcomputer of the present invention, and described main program comprises the initialization 4 of single-chip microcomputer relevant register, pulse acquisition 5, waits for real-time clock interruption 6, and pulse acquisition and compensation interrupt service program. MCU initialization 1 completes MCU port setting, timer/counter 0 and 1 working mode, initial value setting, real-time clock timing initial value setting, etc. Pulse acquisition 2 starts the real-time clock and counter C0, starts counting the pulses input by the pulse input unit, and waits for the real-time clock interrupt 6. When the real-time clock generates an interrupt request, the interrupt service routine is executed. The interrupt service routine executes the collection of input pulses, compares whether the collected pulses are within the compensation range, and completes the non-linear compensation of pulses.

Figure 3 is a flow chart of pulse acquisition and compensation interrupt service program in the present invention, described pulse acquisition and compensation interrupt service program includes acquisition pulse frequency preservation 7, calculation and table look-up correction 8, timer T1 timing initial value calculation 9, The real-time clock is assigned an initial value of 10. Collect the pulse frequency and save 7 to save the register value of the counter C0. Calculation and table look-up correction 8. First, determine whether the collected pulse frequency is within the compensation range. If the collected frequency is within the compensation range, the compensated output pulse frequency is obtained by looking up the table; otherwise, the output pulse frequency is equal to the collected input frequency. Timer T1 timing initial value calculation 9, according to the output pulse frequency after compensation, calculate the timing initial value of timer T1. At the same time, the counter C0 is cleared to 0, and the initial value of 10 is assigned to the real-time clock again.

Figure 4 is a flowchart of the pulse output interrupt service program after compensation in the present invention. The compensated pulse output interrupt service program includes I/O port inversion 11 and initial value assignment 12 . The method of realizing the pulse output is: the timing time of the timer T1 is half of the output pulse period, and then the I/O port is reversed in the interrupt service program of T1. After inversion, re-assign an initial value to T1 to output a continuous square wave.

Claims (2)

1. the turbine flow sensor preamplifier with nonlinear compensation, it is characterized in that, comprise shaping amplification circuit, signal input processing unit, NXP51 series monolithic, output signal processing unit, cell winding induces magnetic flux alternating signal, produce alternation induced potential, first after shaping amplification circuit, send into signal input processing unit, after signal input processing unit does amplitude limit, filtering, Shape correction to signal, send into NXP51 series monolithic again and carry out nonlinear compensation computing, then exported by output signal processing unit.

2. the compensation method of the turbine flow sensor preamplifier according to claim 1 with nonlinear compensation, is characterized in that, comprises the steps:

1) NXP51 series monolithic is according to n calibration point (f _i, K _i, i=1,2 ..., (n-1) bar straight line n) can be obtained, the i-th (i=1,2,3 ... n-1) the instrument coefficient K linear equation of section is:

$K=\frac{K_{i+1}-K_i}{f_{i+1}-f_i}\×(f-f_i)+K_i$

F _i, K _ibe respectively the output frequency of the turbine flow transducer of the i-th flux scale fixed point and corresponding instrument coefficient, the pulse frequency f recorded, divided by the instrument coefficient K calculated through above formula, just can obtain the flow q after nonlinear compensation ₀for:

$q_0=\frac{f}{K}$

Export the pulse frequency f after compensating _outfor:

$f_{out}=\stackrel{\‾}{K}f\×\[\frac{f_{i+1}-f_i}{(f-f_i)(K_{i+1}-K_i)+K_i(f_{i+1}-f_i)}\]$

In formula, f is the frequency that transducer detects;

for compensating the average instrument coefficient in range ability,

In formula, K _max,k _minbe respectively in the n point calibration point compensated in range ability, the maximum of instrument coefficient and minimum value, form the sensor frequency f and compensation afterpulse frequency f that detect _outthe table of comparisons;

2) cell winding induces magnetic flux alternating signal, produce alternation induced potential, i.e. electric impulse signal, NXP51 series monolithic is sent into after shaping amplification circuit, signal input processing unit, NXP51 series monolithic calculates incoming frequency, judging incoming frequency whether in compensation range, in this way, then according to step 1) gained table finds corresponding compensation afterpulse frequency f _out, exported by output signal processing unit; If not, then export after the incoming frequency calculated directly being outputted to output signal processing unit.